Device for secure transmission recording and visualisation of audiovisual programmes

ABSTRACT

A method of distributing video sequences according to a nominal flow format including a succession of frames each including at least one I block corresponding to a complete digital I image and at least one N block corresponding to differences between a digital N image and at least one other image including analyzing the flow of sequences to generate a first modified flow having a format of a nominal flow and having modified N blocks and a second flow of any format including digital information required to reconstruct the modified blocks; and transmitting the first and second flows from a server to destination equipment, and calculating on the destination equipment a synthesis of a flow in a nominal format as a function of the first flow and the second flow.

RELATED APPLICATION

This is a §371 of International Application No. PCT/FR03/00122, with aninternational filing date of Jan. 15, 2003 (WO 03/063445, published Jul.31, 2003), which is based on French Patent Application No. 02/00635,filed Jan. 18, 2002.

FIELD OF THE INVENTION

This invention pertains to the secure processing, broadcasting,recording and display of video data and television programs or moregenerally any multimedia program or sequence using a MPEG type nominalflow format, by authorized users and provides a secured system for theprocessing, broadcasting, delivery, recording, private copying andviewing of video or interactive multimedia programs and sequences.

BACKGROUND

The general problem is to provide a device capable of transmitting in asecure manner a set of high visual quality films in an MPEG type formatdirectly to a television screen and/or to be recorded on the hard diskof a box connecting the remote transmission network to the televisionscreen, while preserving the audiovisual quality but preventing anyfraudulent use such as the possibility of making pirate copies of filmsor audiovisual programs recorded on the hard disk of the decoder box.

With the presently available solutions, it is possible to transmit filmsand audiovisual programs in digital form via broadcast networks of theairwaves, cable, satellite, etc. type or via DSL (Digital SubscriberLine) type telecommunication networks or LRL (local radio loop) networksor via DAB (Digital Audio Broadcasting) networks. Moreover, in order toprevent pirating of works broadcast in this manner, these works areoften encrypted by various means well known to the expert in the field.

However, the principal disadvantage of presently available solutionssuch as in WO 00/165762 is that it is necessary to transmit not only theencrypted data to the users but also the decryption keys. Transmissionof the decryption keys can be performed prior to, at the same time as orafter transmission of the audiovisual programs. In order to increase thesecurity and thus the protection of the audiovisual works againstill-intentioned use, the decryption keys as well as the decryptionfunctions of the audiovisual decoders can comprise enhanced securitymeans such as smart cards or other physical keys that can optionally beupdated remotely.

Thus, the presently available solutions applied to a decoder box withthe ability of local recording of audiovisual programs in digital formon a support of any type such as a hard disk or other type of memoryprovides an ill-intentioned user the possibility of making unauthorizedcopies of the programs recorded in this manner because at any givenmoment this user has with his digital decoder box associated or not withsmart card systems all of the information, software programs and dataenabling the complete decryption of the audiovisual programs. Preciselybecause of the fact that he possesses all of the data, theill-intentioned user would have the possibility of making illegal copieswithout anybody becoming aware of this fraudulent copying when it isperformed.

One solution would therefore consist of transmitting all or part of adigital audiovisual program solely on demand (on demand video services)via a broad-band telecommunication network of the DSL, cable orsatellite type without authorizing the local recording of theaudiovisual programs. The disadvantage there is completely different andstems from the performances of these network which do not make itpossible to guarantee continuous flows of several megabits per second toeach user as required by MPEG flows which require pass bands fromseveral hundreds of kilobits to many megabits per second.

Under these conditions, one solution consists of separating the flowinto two parts neither of which could be used by itself. Many patentshave been filed in the context of this approach. We thus know from WO09/908428 a method for the multiapplication processing of a localizableactive terminal in which there is implemented at least one link with anidentifiable program dedicated to the execution of an application, saidprogram dictating its operating conditions to the terminal for thesetting up of its functions. The terminal dialogues in a punctiformmanner by using a link with the management center for theimplementation, if necessary, of the inputs and outputs of thecapacities of this center with the management center optionally becomingthe slave of the terminal at the application level in relation to theincoming program. That invention also pertains to the method for theidentification of the program and the terminal in operating mode. Thatmethod of the prior art divides the flow into a part used foridentifying the user and a part that contains the actual program itself.In particular, the program is not unusable but merely made inaccessibleby the first part.

In addition, EP 0778513 describes a method enabling prevention ofillegal use of an information unit by adding to it a control informationunit in order to verify the rights of the user. The system makes itpossible to remain permanently informed as to which part of theinformation unit is used and by which user and thereby to be informed asto whether or not this user is in an illegal position. That method thusmakes the data secure by adding additional information units whichdistort the initial information.

WO 00/49483 also provides methods and systems for creating a linkbetween the users and an editor of digitized entities. The methodcomprises at least one of the following steps: the step of subdividingsaid digitized entity into two parts; the step of storing one part inmemory in a server connected to a computer-based network; the step oftransmitting the other part to at least one user who has availablecomputer-based equipment; the step of connecting said computer-basedequipment to said computer-based network; the step of establishing afunctional link between said first part and said second part. Thosemethods and systems do not specify whether the part stored in memory onthe server can be stored by the user, which would enable the user topirate said digitized entity.

Lastly, with regard to this approach, the closest state of the art isfound in the patents of HyperLOCK Technologies, the most pertinent ofwhich is U.S. Pat. No. 5,937,164. That invention uses the solutioncomprised of separating the flow into two parts, the smaller one ofwhich holds an information unit required for the use of the larger part.That patent nevertheless is not sufficient for resolving the identifiedproblem. In fact, suppression of a part of the flow distorts the formatof the flow which then cannot be recognized as a standard flow that canbe run with general software applications. That method of the prior artrequires both a specific software program at the server side for theseparation of the two parts, and another specific software programenabling not only the reconstruction of the flow but also theacquisition of the principal flow and its management according to aformat proprietary to the solution. That proprietary format is not theinitial format of the flow prior to separation into two parts in thisknown solution.

U.S. Pat. No. 5,892,825 returns to the approach of the preceding patentbut in a narrower framework because the flows are still encrypted; U.S.Pat. No. 6,035,329 is based on the same principle and pertains to amethod enabling the reading of a CD-ROM or DVD-ROM disk contingent onthe identification of the rights by the insertion of a smart card onwhich the information required for reading are stored. That method isstill not adequate for our problem because it does not ensure that themodified flow is of the same format as the original flow. Finally, U.S.Pat. No. 6,185,306 pertains to a method for the transmission ofencrypted data from a Web site to a requesting computer. That method,however, makes it possible for the user to have available at a givenmoment the tools required for copying the data.

SUMMARY OF THE INVENTION

This invention relates to a method of distributing video sequencesaccording to a nominal flow format including a succession of frames eachincluding at least one I block corresponding to a complete digital Iimage and at least one N block corresponding to differences between adigital N image and at least one other image including analyzing theflow of sequences to generate a first modified flow having a format of anominal flow and having modified N blocks and a second flow of anyformat including digital information required to reconstruct themodified blocks; transmitting the first and second flows from a serverto destination equipment, and calculating on the destination equipment asynthesis of a flow in a nominal format as a function of the first flowand the second flow.

This invention also relates to a system that creates a video flowaccording to the method, including at least one multimedia servercontaining original video sequences and a device for analyzing videoflow originating from the server for generating the first and secondflows.

This invention further relates to a system that manages a video flowaccording to the method, including a computer unit of a communicationinterface for receiving the video flow originating from a communicationnetwork or a physical support reader and equipped with at least onerecorder that stores content of the first flow, a decoder including adisplay interface, means for communicating with the principal computerfor receiving the first flow transmitted by the computer andcommunication means for receiving the second flow, and a means forrecomposing original flow from the first and second flows.

This invention yet again relates to a system for transmitting a videoflow according to the method, including an equipment unit that producesa video flow, at least one equipment unit that manages the video flowand at least one communication network between the production equipmentand the management equipment unit(s).

BRIEF DESCRIPTION OF THE DRAWINGS

Better understanding of the invention will be obtained from thedescription below of a nonlimitative example of implementation withreference to the attached drawings in which:

FIG. 1 describes the architecture of a system for the implementation ofthe method according to the invention; and

FIG. 2 represents one particular mode of implementation of the systemfor the analysis and synthesis of MPEG type flow in accordance with theinvention.

DETAILED DESCRIPTION

This invention pertains in its broadest sense to a method for thedistribution of video sequences according to a nominal flow formatconstituted by a succession of frames each comprising at least one Iblock corresponding to a complete digital I image and at least one Nblock corresponding to the differences between one digital image and atleast one other image, characterized in that there is performed prior tothe transmission to the client's equipment an analysis of the flow inorder to generate a first modified flow presenting the format of anominal flow and having modified N blocks and a second flow of anyformat comprising the digital information which can enable thereconstruction of the modified blocks, then of separately transmittingthe two flows thereby generated from the server to the destinationequipment, and in that there is calculated on the destination equipmenta synthesis of a flow in the nominal format as a function of said firstflow and said second flow.

The synthesis advantageously produces a flow rigorously identical to theoriginal flow, i.e., the process is without loss.

According to one particular mode of implementation of this method, atleast one N block corresponds to an N image calculated by movementcompensation in relation to the preceding N or I image. The block andimage are then referred to as P block and image (predicted).

According to another mode of implementation of this method, at least oneN block corresponds to an N image calculated by movement compensation inrelation to the preceding and following P or I images. The block andimage are then referred to as B block and image (bidirectional).

If there are B and P images, an N block is necessarily of type B or typeP.

According to one particular variant of this method, the nominal flowformat is defined by the MPEG standard.

The analysis can advantageously determine the N images to be modified inorder to obtain the first flow; these modifications can be: replace a Pimage by another P image from another flow, invert two P images of thesame flow, invert a B image and a P image of the same flow.

In one particular implementation of this method, the transmission of thefirst flow is implemented via a material support distributed physicallysuch as a CD-ROM, a DVD or a hard disk.

In another implementation of this method, the transmission of the firstflow is implemented via a broad-band network (cable, satellite, opticalfiber, airwaves) via a DSL (Digital Subscriber Line) type network, via aDAB network or via a local radio loop network (LRL).

According to the implementation of this method, the transmission of thesecond flow is implemented via a cable network, via a switchedtelephonic network (analog or digital), via a mobile telephonic networkusing the GSM, GPRS or UMTS standards, via an LRL network (local radioloop) or via a DSL network.

According to one particular variant of this method, transmission of thesecond flow is implemented via a broad-band network of the same type asthe network used for the first flow, or via the same network.

Transmission of one or both of the two flows is advantageouslyencrypted.

One or both of the flows can advantageously be watermarked.

According to one particular mode of implementation, reconstruction iscontingent on a payment.

Reconstruction can also be authorized by consultation of a private copydemanded by the client.

The invention moreover pertains to an equipment unit for the creation ofa video flow for the implementation of this method comprising at leastone multimedia server containing the original video sequences andcharacterized in that it comprises a device for the analysis of thevideo flow stemming from the server in order to generate the two flows.

This equipment advantageously comprises a memory for recording a“private copy” marker indicating for each sequence the rights of eachuser: private copy that can be watched an unlimited number of times,private copy that can be watched a limited number of times andspecification of that number, and private copying prohibited.

The invention moreover pertains to equipment for the management of avideo flow for the purpose of implementing this method comprising astandard flow decoder, at least one recording interface (hard disk,flash memory, etc.) intended to store the contents of the first flowand/or a disk reader (CD, DVD, etc.) and at least one display interface(standard screen, wireless screen, video projector), characterized inthat it comprises a means for the recomposition of the original flowfrom the two flows.

According to one particular mode of implementation, the means is asoftware application installed in the equipment.

According to another mode of implementation, the means is a fixedelectronic device.

According to another mode of implementation, the means is a portable ormobile electronic device.

According to a mode of implementation in which the equipment isinstalled on a computer, the means uses a resource specific to theproduct (card) so as to prevent the copying of the temporary informationof the second flow onto a permanent support.

The recording interface advantageously also stores a “private copy”marker in relation to the first flow indicating for this sequence therights of the user: private copy that can be viewed an unlimited numberof times, private copy that can be watched a limited number of times andspecification of that number, private copying prohibited.

The equipment advantageously comprises a smart-card reader foridentifying the user.

The equipment advantageously comprises a smart-card reader, the smartcard containing the software applications and/or the data of said secondflow.

One variant of implementation consists of implementing the clientequipment in the form of two means interconnected by a physical link ora remote link (Bluetooth, AirPort, WiFi, infrared, etc.). According tothis variant, the equipment for the management of a video flow comprisesa first means constituted by a personal computer of a communicationinterface for receiving a video flow originating from a communicationnetwork or a physical support reader, and equipped with at least onerecording means [hard disk] intended to store the content of said firstflow, and a second means constituted by a decoder comprising a displayinterface, means for communication with said principal computer forreceiving said first flow transmitted by the computer and communicationmeans for receiving said second flow, as well as a means for therecomposition of the original flow from the two flows.

According to a first mode of implementation, the means for therecomposition of the flow is a software application installed solely onthe decoder.

According to a second mode of implementation, the means for therecomposition of the flow is an electronic device installed solely onthe decoder.

Lastly, the invention pertains to a system for the transmission of avideo flow, characterized in that it comprises an equipment unit forproduction of a video flow, at least one equipment unit for managementof a video flow and at least one communication network between theproduction equipment and the management equipment.

The invention pertains to a flow of data of a nominal format especiallybut not exclusively a flow of the MPEG type. The format of theaudiovisual flow used must have the following characteristics:

-   -   this format must break down the data into frames, each frame        comprising a complete digital I image and at least one P image        calculated by coding the differences (movement compensation)        between this image and the preceding I or P image;    -   optionally, each frame comprises at least one B image calculated        by coding the differences (movement compensation) between this        image and the preceding and following I and/or P images.

In the description below the example pertains to an MPEG flow; this doesnot however constitute a limitation on the scope of protection.

The general principle of a method to ensure the security of a video flowis presented below. The objective is to authorize on demand video andupon demand via all of these broadcasting networks and the localrecording in the user's digital decoder box. The solution consists ofpermanently preserving outside of the user's habitation, in fact in thebroadcasting and transmission network, a part of the recordedaudiovisual program, this part being essential for viewing theaudiovisual program on a television or monitor screen, but being of verysmall volume in relation to the total volume of the digital audiovisualprogram recorded by the user. The missing part will be transmitted viathe broadcasting and transmission network at the time of viewing saiddigital audiovisual program prerecorded by the user.

The greatest part of the MPEG audiovisual flow will thus be transmittedvia a conventional broadcast network while the missing part will be senton demand via a narrow-band telecommunication network such asconventional telephone networks or using a small part of a DSL or LRLtype network, or using a subset of the shared pass band on a cablenetwork.

FIG. 1 in the attached drawings is a diagram of the principle of adistribution system according to the present invention.

FIG. 2 represents a particular mode of implementation of the system forthe analysis and synthesis of MPEG flow according to the invention.

In FIG. 1, the video interface (8) setup is adapted for connecting atleast one display device, e.g., a monitor, a video projector or atelevision screen type device (6) to at least one broad-bandtransmission and broadcasting network (4) interface and to at least onetelecommunication network interface (10). According to the invention,this setup is composed of a module (8) comprising principally a suitableprocessing unit for processing, in particular decoding and unscrambling,all MPEG type video flows according to a preloaded decoding andunscrambling software program in real or delayed time, of storing it,recording it and/or transmitting it on a telecommunications network, aswell as a screen interface (7) and an interface for connection to alocal or extended area network (5) and/or (9). The broad-bandtransmission and broadcasting network (4) and the telecommunicationnetwork (10) can be a single network.

The hard disk of the module (8) can be used as a buffer memory formomentarily storing at least a part of the video program or sequence tobe displayed in the case of delayed display or of limitation in the passband of the transmission network. Viewing can be delayed or differedupon request of the user or the portal (12).

As shown in FIG. 1, the connection interface (5) is linked to abroad-band transmission and broadcasting network (4) such as a modem, asatellite modem, a cable modem, an optical fiber line or a radio orinfrared interface for wireless communication.

It is by means of this conventional video broadcasting link that thecontents of audiovisual programs such as films will be transmitted.Nevertheless, in order to prevent the possibility of pirate copies,prior to transmitting the audiovisual content from the server (1) orportal (12) it is provided to hold back a small part of the audiovisualcontent in the portal (12).

In the case of viewing an audiovisual program in real time, this smallpart of the audiovisual content preserved in the portal (12) will alsobe sent to the module (8) via the telecommunication network (10).

Since the successive images of a video sequence contain a large numberof identical visual elements (as with cinema, an image resembles thepreceding image), MPEG only records the elements that differ from theoriginal image. Thus, there is preserved an entire reference image and,for the successive images, only the modifications are retained.

Thus, the MPEG compression commences initially by breaking down theimage into different square matrices comprising multiple points orpixels, each having its own colorimetric value. A calculation makes itpossible to obtain an average value for each matrix within which eachpoint is maintained in embedded form. This process generates apixellation and the appearance of uniform tints where tint nuancespreviously existed. The second step of the MPEG compression consists ofpreserving from one image to another only the changing elements.

In order to obtain animated images, the principle consists of capturingseveral images in time, while the intermediary images are calculatedfrom these images. Analysis of the complete reference images (referredto as I images=Intra-frame images) enables prediction of theintermediary P images (Predicted frames). Then, the B images(Bidirectional frames) are intercalated between the reference images andthe predicted images.

Three major types of images are thus defined in order to respond to thecontradictory demands of a possibility of direct access and a highcompression efficacy.

1. The Intra coding images (I images) are coded without reference to theother images. They provide the access points to the coded sequence inwhich the decoding can commence but are coded with a moderatecompression rate.

2. The Prediction coded images (P images) have a more effective codingusing a movement-compensated prediction after a prior intra (I) orpredicted (P) image, and are generally used as reference for a futureprediction.

3. The images coded by Bidirectional prediction (B images) provide thehighest compression rate, but require for movement compensation a priorreference image and a future reference image. The images coded bybidirectional prediction are never used as prediction reference.

The organization of the three kinds of images in a sequence is veryflexible: its selection is left to the coder and depends on therequirements of the application.

When it reads the binary train, a conventional MPEG decoder identifiesthe beginning of a coded image, then the type of image. In order toavoid any confusion between a standard decoder box (often referred to asa “Set Top Box” or STB), the standard MPEG decoder will be referred toas the “Reader” (“Player” or “Viewer”) in the document below. ThisReader can be implemented in hardware or software form. The MPEG readerdecodes successively each macroblock of the image. The image isreconstructed when all of its macroblocks have been processed. In thecase of an I image or a P image, it constitutes a reference image forthe subsequent images and it is stored in the place of the oldestreference image. The images are thus available in digital form forpost-processing and display, according to the application.

In the case of an MPEG type audiovisual program, it is provided to nottransmit all of the B and/or P images originating from the server (1) orthe portal (12) to the module (8). These B and/or P images beingretained in the portal (12). To the contrary, in the place of theuntransmitted B and/or P images, the device according to the inventionintercalates false B and/or P images of the same type as the removed Band/or P images and retained in the portal (12) such that the standardMPEG Reader of the module (8) is not disturbed by these modificationsthat it will be unaware of and it will reconstitute as output anoutgoing MPEG flow that will be incorrect from the visual point of viewfor a human being but correct from the MPEG format point of view.

The MPEG Reader of the box (8) is a standard MPEG Reader and has notbeen changed in any way or affected by the changes performed on the Band/or P images.

According to one particular mode of implementation, in order to increasethe efficacy of the protection system it is preferable to not send the Band/or P images which are closest to and which follow the I images ofthe MPEG flow. For even greater efficacy, after analysis of their volumeand their weight in octets or in bits, B and/or P images will beselected to not be transmitted but retained in the portal (12).

According to one particular mode of implementation, certain P and/or Bimages will be permuted among each other.

As shown in FIG. 1, the connection interface (9) is linked to anextended telecommunication network (10) directly or via a local networkserving as access network and it is constituted, e.g., by a subscriberline interface (analog or digital telephonic network, DSL, LRL, GSM,GPRS, UMTS, etc.).

Thus, the audiovisual programs are broadcast in a conventional manner inmultidiffusion mode (“broadcast”) via the broad band transmissionnetwork (4) of the airwaves, cable, satellite, digital airwaves, DAB,DSL type, etc., from the server (1) directly via the link (3 bis) or viathe portal (12) via the link (2) and (3) to the decoder module (8) bymeans of the link (5). Each audiovisual program broadcast in this mannercan be optionally encrypted and in accordance with the invention, theMPEG flow contains modifications at the level of the B and/or P imagesas described above. As a function of the parameters selected by the useror of the information transmitted by the broadcast server, certainaudiovisual programs modified in this manner and incomplete are recordedon the hard disk of the box (8).

When the user wants to watch an audiovisual program recorded in thismanner on the hard disk of his box (8), he issues the command in theconventional manner via the remote control linked to his box (8) whichthen connects automatically to the portal (12) via the link (9) of thelocal network or direct access type and via the telecommunicationnetwork (10) which is itself linked to the portal (12) via the link(11). During the entire displaying of the audiovisual program, the links(9) and (11) remain connected and allow the box (8) to receive themissing B and/or P images as well as the algorithms, functions andparameters for restoring the order of the B and/or P images. The Band/or P images transmitted in this manner are never recorded on thehard drive of the box (8) but are directly displayed on the displayscreen (6) via the link (7) after having been processed by the Reader ofthe box (8) from its local volatile memory. Once they have beenprocessed and displayed, the B and/or P images having been transmittedby the portal (12) will be erased from the local volatile memory of thebox (8).

According to a particular mode of implementation, the P and/or B imagesbroadcast in this manner can be optionally encrypted by any existing orfuture encryption means. The same is true for the algorithms, functionsand parameters for restoring the order of the B and/or P images.

Each time that the user wants to watch a program recorded on the harddisk of the box (8), the box (8) will connect automatically to theportal (12). The same is true when the user pauses, the transmission ofthe B and/or P images originating from the portal (12) will beinterrupted until the restarting of the display, thus ensuring that notall of the information units of an audiovisual program will be found inthe box (8) at a given moment and thereby preventing an ill-intentionedperson from making pirate copies of these recordings.

According to a particular mode of implementation, the box (8) comprisesa smart card reader which enables the portal (12) to authenticate theuser owner of the box (8). If this is authorized, this function alsoallows the user to make private copies of the audiovisual programsrecorded on the hard disk of his decoder box (8). In order to do this,if the user wants to make a private copy of an audiovisual program, theuser does so in the conventional manner on a VCR via the link (7) thatconnects the box (8) to the display screen (6).

However, if the user wants to preserve a private copy on the hard diskof the box, the user will so inform the box (8) which will record the“private copy” information unit as well as the coordinates of the userwhich are on the smart card in a particular field (84) of thisaudiovisual program recorded on the hard drive (85) of the decoder box(8). Whenever the user subsequently wants to watch this private copy,the box (8) will connect automatically to the portal (12) and inform thebox that the user wants to implement a reading of his private copy; inresponse, if the reading of the private copy is possible for this userwho possesses this smart card linked to this box (8), the decoder box(8) will then receive the missing B and/or P images as well as all theother information enabling the display of the audiovisual programconstituting the private copy.

According to another mode of implementation, if the user wants topreserve a private copy on the hard drive of the box, the user will soinform the server which will record the information unit “private copy”for this program and for this user authenticated by the smart card. Eachtime that the user wants to watch this private copy, the box (8) willthen connect automatically to the portal (12) and will inform thisportal that the user wants to implement a reading of the user's privatecopy; in response, if the reading of the private copy is possible forthis user who possesses this smart card and for this program, thedecoder box (8) will then receive the missing B and/or P images as wellas all of the other information enabling the viewing of the audiovisualprogram constituting the private copy.

According to a particular mode of implementation, the so-called “privatecopy” could enable the user to watch this same audiovisual program in anunlimited manner or a number of times determined in advance by theservice provider who authorized this private copy.

The invention also pertains to the physical box (8) used by the consumerto access the data. This physical box is located at the user's domicile.It provides a set of functionalities which manage the appropriateinformation to be presented according to the audience's selection andmanages the connection and communication with the remote server.

According to a particular mode of implementation, the physical box (8)corresponding to the video interface setup is implemented as a fixedautonomous device with integrated hard disk.

According to another particular implementation, the video interfacesetup is implemented as an add-on card which would be installed in aPC-type computer and would be linked to at least one broad-bandtransmission and broadcasting network interface (4) and to at least onetelecommunication network interface (10). This card would use the harddisk of the PC for recording the first flow, but would have its owncalculator and its own volatile memory so as to not allow theill-intentioned user of the PC the means to access the complementaryinformation units such as the B and/or P images of the second flow.

According to the present invention, the video and multimedia servers (1)and/or (12) comprise the means for coding, transcoding and scrambling ofvideo data, in particular the means for adding cryptographic andsecurity information units at the beginning and all along the sequences.

It lastly should be noted that the invention degrades the MPEG flow fromthe visual point of view until no longer allowing recognition of thetransmitted and displayed scenes without having access to thecomplementary data and characteristics, but completely reconstitutes theMPEG flow in the video interface setup without any loss.

Although the invention has focused most particularly on audiovisualdata, it is understood that all interactive multimedia information andall interactive data can be processed by the setup and the system, MPEGtype video data being the most elaborated. Better understanding of theinvention will be obtained from the description below describing thephysical basis of the invention and with reference to FIG. 2 of theattached drawings representing a preferred mode of implementation ofthis latter setup as a nonlimitative example of implementationparticularly suitable for cable and satellite networks. The completeMPEG flow (101) is analyzed by the analysis device (121) of the portal(12) and will thus be separated into an MPEG type flow but whose Band/or P images will have been processed and sent via the output (122)of the portal to the broad band transmission and broadcasting network(4).

The other part of the modified MPEG flow will be stored in memory in thebuffer memory (122) of the portal (12). For each MPEG flow broadcast inthis manner, the portal (12) will store in a buffer memory (122) themodifications that were implemented in this MPEG flow by the analyzer(121) of the portal (12). It should be clarified that for the sameincoming MPEG flow (101) the processing of the flow can be different foreach user (18) and/or for each group of users (18). Thus, the buffer(123) of the portal (12) comprises a different memory zone for eachuser.

In the implemented examples, for a first user (18) each first P image ofthe MPEG flow which follows an I image was replaced by a random P imageof the same type and same volume as the P image removed in this manner.It has been found that the degrading effects on the output flow are veryintense.

For a second user (18) the nth P image that follows each I image of theMPEG flow was permuted by and with the first B image that follows this Pimage. It has been found that this permutation is very effective forMPEG type animated sequences compared to MPEG sequences having littleanimation.

We will now describe in detail the different steps for this first user.

The portal (121) selected the MPEG flow (101) that it must transmit tothe user (18) to be watched on a delayed basis on his television screen(6). This user is linked to a digital cable broadcast network (4)offering video on demand (VOD), the network (10) is thus the same as thenetwork (4). The analysis system (121) of the portal (12) will thus readthe incoming MPEG flow (101) and each time that it detects an I image,it searches for the first P image that follows this I image so as toreplace it with a random P image that it calculated. The new modifiedMPEG flow is then recorded in the output buffer (122) to be broadcast onthe broadcast network (4) via the link (5). The P images removed fromthe incoming MPEG flow (101) are stored in the buffer memory (123) ofthe portal. In the implemented example, rather than substitute each Pimage that follows an I image, the analysis system (12) only takes one Iimage out of n in which n is a random number comprised between 1 and 7.When the analysis system (121) writes the substituted P image in thebuffer memory (123), it also writes the number of the I image thatprecedes the thereby substituted P image. The analysis system (121)continues its analysis until the end of the incoming MPEG flow.

During this time and in a completely unsynchronized manner, the outgoingmodified MPEG flow originating from the output buffer (122) of theportal (12) is broadcast via the broad band network (4) to one or moreusers (18).

Each decoder box (8) from FIG. 1 (that is essentially a user 18 in FIG.2) that wants to record this MPEG flow modified in this manner can thenread this MPEG flow and record it on its hard disk (85). This recordinginitiative is left to the decoder box (8) under the control of theportal (12). In order to perform this, the analysis system (121) hadwritten at the beginning of the MPEG flow an information unit ofsupplementary data that specified the addresses of this modified MPEGflow. The addressees can thus be a particular and single addressee/user(18), a group of addressees/users (18) or the totality of the decoderboxes (8) from FIG. 1 linked to the network (4).

The phase described above corresponds to the first phase of preparationof the MPEG flow by the portal (12), its transmission via the broad bandnetwork (4) and its recording in a decoder box (8) from FIG. 1. Thisdecoder can then display this MPEG flow recorded on its hard disk (85).In order to perform this, the synthesis system (87) of the decoder box(8) in FIG. 1/user (18) will read the MPEG file from its hard disk (85)and will send it to a conventional MPEG reader (81). If no complementarydata is received by the synthesis system (87), then the MPEG flow whichreaches the reader (81) is processed and displayed as it is, whichcauses a huge distortion of the display on the display screen (6). Ineffect, the substituted P images which are processed by the synthesissystem (87) do not correspond to the P images which are required for acorrect viewing because certain P images were replaced by random Pimages. In contrast, since the recorded flow is definitely an MPEG typeflow, the reader (81) does not discriminate and displays the informationon the output screen (6) where it gives the appearance of an MPEG videoflow but which is totally incoherent for the human being who watches thescreen (6). Any copy of the MPEG flow originating from the hard disk(85) of the box (8)/user (18) would produce the same visual effect whenit is reconstituted by any MPEG reader; all uses of this copy whichwould be ill-intentioned are thus doomed to failure.

When the user (18) wants to correctly display on his screen (6) theaudiovisual program recorded on his hard disk (85), the user sends arequest to the synthesis system (87) with a remote controller as with aVCR or DVD reader presenting a menu on a television screen. Thesynthesis system (87) then issues a request to the hard disk (85) andcommences to analyze the modified MPEG flow originating from the harddisk (85) via the reading buffer (83). The synthesis system (87) thenestablishes a link with the portal (12) via the telecommunicationnetwork (10) which in the example is also the cable network, but whichcan be a conventional telephone network or a DSL link. Once this linkhas been established, and during the entire duration of watching thefilm or audiovisual program, the synthesis system (87) draws out fromthe buffer memory (123) of the server (12) the substituted P images andthe data corresponding to the positions of these P images in relation tothe I images of the flow recorded on the hard disk. These P images andthese position data are drawn out from the synthesis system (87) via theinput buffer memory (86) and are stored temporarily in the volatilememory (88) of the synthesis system (87). From the modified MPEG flowthat is drawn out via the buffer (83) and from the P images and theassociated data that are drawn out via the buffer (86) in the memory(88), the synthesis system reconstitutes, in reverse manner of thepreviously described analysis process, the P images substituted by thereal P images and sends the thereby reconstituted new MPEG flow to thereader (81) to be displayed correctly on the screen (6). Upon their use,the P images to be substituted and the data associated with these Pimages are erased from the volatile memory (88).

In the implemented example, before the portal (12) authorized thetransmission of the P images and the associated data from its buffer(123), the portal (12) had verified that the user (18) was in factauthorized to receive them. In order to implement this step, the portal(12) reads the information contained on the smart card (82) of the user(18)/box (8) and verifies that the user is in fact authorized to watchthis audiovisual program. It is not until this verification has beenperformed that the P images and the associated data are sent from thebuffer (123) to the box user (18)/(8) corresponding to this user.

In the implemented example, the user had made a private copy of hisaudiovisual program. The synthesis system (87) therefore wrotecomplementary data on a part (84) of the hard disk (85) as well as thenumber of the smart card (82) and the information unit “private copy” asdata associated with this audiovisual program. Upon the next privatereading of this audiovisual program, the synthesis system (87) willanalyze these associated data and then inform the portal (12) that theuser (18) is implementing a reading of the private copy. If thisfunction is authorized for this user (18) by the portal (12), the Pimages and the associated data will then be sent by the portal (12) tothe buffer (86) as described above. In the contrary case, the data willnot be sent and the user (18) will not be able to watch thereconstituted MPEF flow.

We will now describe in detail the different steps for the second user(18).

In this second case, the broadcast network (4) is a satellite networkand the telecommunication network (10) is an airwaves system of thelocal radio loop (LRL) type.

In a manner identical to the description above, the user (18) willreceive the MPEG flows and the complementary data from the portal (12).In contrast, before sending the MPEG flow from the output buffer (122),the analysis system (121) will read the incoming MPEG flow (101) anddrawing a random number n comprised between 1 and 4, the synthesissystem permutes the nth image P which follows each I image of the MPEGflow with the first B image that follows this P image. Each randomnumber used in this manner is recorded in the buffer memory (123) of theportal (12).

During the reconstitution of the MPEG flow by the synthesis system (87)of the decoder box (8), the reading of these random numbers from theportal (12) and the reading of the MPEG flow modified in this marinerfrom the hard disk (85) of the box (8) enables the synthesis system (87)to restore the B and P images in the correct order and send all of it tothe reader (81).

1. A method of distributing video sequences in a coded stream includinga succession of images each comprising at least one Intra-frame codedimage (I picture) and at least one Prediction coded image correspondingto differences between at least two images of the succession of imagescomprising: analyzing an original coded stream prior to transmission toan input/output device of a client and generating, based upon theanalysis, a first modified stream and a second stream, wherein saidfirst modified stream includes a modified Prediction coded image, saidmodified Prediction coded image being a randomly generated image or theresult of swapping two Prediction coded images, so that the modificationfrom said at least one Prediction coded image results in a visuallyaltered video sequence, and an I picture, which is not modified, saidfirst modified stream maintaining a form for an encoding system appliedto said original coded stream after said modification, and said secondstream including digital information that allows a reconstruction fromsaid modified Prediction coded image to said original coded stream;separately transmitting the two generated streams from a server to adestination device; and synthesizing said first modified stream and saidsecond stream at the destination device to reconstruct said originalcoded stream.
 2. The method according to claim 1, wherein saidPrediction coded image is an interframe Prediction coded image and/or abidirectional Prediction coded image calculated by motion compensationfrom a previous or subsequent interframe Prediction coded image or the Ipicture.
 3. The method according to claim 1, wherein said second streamincludes a pre-modification image that corresponds to the modifiedPrediction coded image in said first modified stream; and at saiddestination device, the modified Prediction coded image in said firstmodified stream is replaced with the corresponding image in said secondstream in the synthesis of reconstructing said original coded stream. 4.The method according to claim 1, wherein said modified Prediction codedimage is a replacement P picture that is different from, but has thesame data volume as, and replaces a first P picture following the Ipicture.
 5. The method according to claim 1, wherein said modifiedPrediction coded image is a modified Prediction coded image whosemodification is done by replacing an n-th interframe Prediction codedimage (P picture) following the I picture with a first bidirectionalPrediction coded image (B picture) following the P picture.
 6. Themethod according to claim 1, wherein said second stream is distributedvia any of a switched telephone network (analog or digital) and a mobiletelephone network with GSM, GPRS or UMTS.
 7. The method according toclaim 1, wherein said first modified stream is a stream that can bedecoded by a decoder that is itself based on an MPEG standard or iscompliant with an MPEG standard.
 8. The method according to claim 1,wherein said coded stream is a stream that is encoded in an MPEGstandard or is encoded by a method compliant with an MPEG standard; saidIntra-frame coded image is equivalent to I picture in the MPEG standard;and said Prediction coded image is equivalent to P picture or B picturein the MPEG standard.
 9. The method according to claim 1, wherein saidfirst modified stream includes a modified P block that constitutes partof the interframe Prediction coded image (P picture).
 10. A video-streamgenerating system that generates a video stream as a coded streamincluding a succession of frames each comprising at least one Intraframecoded image (I picture) and at least one Prediction coded imagecorresponding to differences between at least two images of thesuccession of images, comprising: at least one multimedia server whichcontains original video sequences; and an analyzing device that analyzesthe video stream originating from an input/output server, said analyzingdevice detecting said Prediction coded image in said video stream andgenerating two streams, one of which is a first modified stream and theother of which is a second stream; wherein said first modified streamincludes a modified Prediction coded image, said modified Predictioncoded image being a randomly generated image or the result of swappingtwo Prediction coded images, so that the modification from said at leastone Prediction coded image results in a visually altered video sequence,and an I picture, which is not modified, said first modified streammaintaining a form for an encoding system applied to said original codedstream after said modification; said second stream including digitalinformation that allows reconstruction from said modified Predictioncoded image to said video stream; and said video-stream generatingsystem, in response to a request from a user, separately transmits saidfirst modified stream and said second stream.
 11. The system accordingto claim 10, further comprising a memory that records a “private copy”marker indicating for each user a right to each video content; whereinsaid right of each user includes a right to watch a private copy of avideo content an unlimited number of times, a right to watch the privatecopy a limited number of times with an indication of the number, or aright prohibiting private copying; said video-stream generating system,in response to a request from a user for privately copying a specificvideo content, providing said first modified stream to said user; andsaid video-stream generating system, in response to a request from saiduser for watching said private copy of the video content, transmittingsaid second stream to said user after confirming the right to the videocontent.
 12. A video-stream playing device for playing a video stream asa coded stream including a succession of frames each comprising at leastone Intra-frame coded image (I picture) and at least one Predictioncoded image corresponding to differences between at least two images ofthe succession of images, comprising: a stream decoder which decodessaid coded stream; at least one recording interface which stores contentof a first modified stream including a modified Prediction coded image,said modified Prediction coded image being a randomly generated image orthe result of swapping two Prediction coded images, so that themodification from said at least one Prediction coded image results in avisually altered video sequence, and an I picture, which is notmodified, said first modified stream maintaining a form for an encodingsystem applied to said original coded stream after said modification; atleast one display interface; and a synthesizing unit that detects saidmodified Prediction coded image in said first modified stream andreconstructs the original coded steam from said first modified streamand a second stream that includes the Prediction coded image, which isnot modified.
 13. The device according to claim 12, wherein saidsynthesizing unit further comprises a memory device for temporarilystoring said second stream; and said second stream stored temporarily insaid memory device is deleted after the original coded stream isreconstructed from said second stream and said first modified stream,which is stored in said recording interface.